Emission control devices are used in vehicles to reduce emissions, thereby reducing a vehicle's environmental impact. Catalysts such as selective catalytic reduction (SCR) catalysts may be utilized in vehicles to achieve this emissions reduction. Additional emission control devices which may be utilized in vehicles include oxidation catalysts, particulate filters, 3-way catalysts, etc. Diesel engines may generate a large amount nitrous oxide (N2O) and other nitrogen compounds which may have a particularly long life in the atmosphere. Thus, the nitrogen compounds, such as N2O, generated in engines may be of particular environmental concern and therefore may be regulated for both commercial and non-commercial vehicles.
U.S. Pat. No. 7,767,175 discloses an after-treatment system having a selective catalytic reduction (SCR) catalyst positioned upstream of a diesel oxidation catalyst (DOC) where ignition temperature in the system is reduced to reduce emissions. However, the inventors have recognized several drawbacks with the after-treatment system disclosed in U.S. Pat. No. 7,767,175. For instance, the after-treatment system may generate a large amount of nitrogen compounds, such as nitrous oxide, due to the positioning of the DOC downstream of the SCR catalyst and the interaction between the two components. Moreover, the material composition of the DOC may also contribute to the increased generation of nitrogen compounds such as N2O.
The inventors have recognized the aforementioned drawbacks of previous emission control systems and have developed an emission control system including an oxidation catalyst having a precious metal loading of less than 100 grams (g)/cubic foot (ft3) and a selective catalytic reduction (SCR) component positioned downstream of the oxidation catalyst operated between 150° C. and 300° C. during engine operation to reduce the formation of N2O in the selective-catalytic reduction component.
It has been unexpectedly found that holding the SCR catalyst with the recited temperature range and providing the recited amount of a precious metal loading in the oxidation catalyst upstream of the SCR catalyst work in conjunction to reduce the emissions from the emission control system. Specifically, the following reaction may take place in the SCR catalyst.2NH3+2NO2→N2O+N2+3H2OWhen the oxidation catalyst is loaded with less than 100 g/ft3 with precious metals the amount of nitrogen oxide (NO2) is reduced, thereby reducing the formation of nitrous oxide in the SCR catalyst. Moreover, maintaining the SCR catalyst temperature within the recited temperature range further reduces the amount of nitrous oxide formation in the SCR catalyst. In this way, emissions from the emission control system are reduced, thereby reducing the vehicle's environmental impact. Therefore, it will be appreciated that the technical results achieved via the aforementioned emission control system include emissions reduction via the interaction between the oxidation catalyst and the SCR catalyst.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Additionally, the above issues have been recognized by the inventors herein, and are not admitted to be known.